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Updated: Jul 4, 2026
09:52
Measuring and Manipulating Functionally Specific Neural Pathways in the Human Motor System with Transcranial Magnetic Stimulation
Published on: February 23, 2020
Mechanisms underlying functional changes in the primary motor cortex ipsilateral to an active hand.
Monica A Perez1, Leonardo G Cohen
1Human Cortical Physiology Section and Stroke Neurorehabilitation Clinic, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892, USA.
Summary
This study reveals how the brain adjusts motor control during unimanual tasks. It shows that short-interval intracortical inhibition (SICI) and interhemispheric inhibition (IHI) change with force, influencing corticospinal output to the resting hand.
Area of Science:
- Neuroscience
- Motor Control
- Human Physiology
Background:
- Unimanual tasks induce functional changes in primary motor cortices (M1).
- Neuronal mechanisms controlling corticospinal output to a resting hand during unimanual tasks are not fully understood.
Purpose of the Study:
- To investigate functional changes in the ipsilateral M1 and interhemispheric inhibition (IHI) during parametric increases in unimanual force.
- To elucidate the neuronal mechanisms underlying corticospinal output control to a resting hand during contralateral force generation.
Main Methods:
- Transcranial magnetic stimulation (TMS) was used to measure motor-evoked potential (MEP) recruitment curves (RCs) and short-interval intracortical inhibition (SICI) in the ipsilateral M1.
- Interhemispheric inhibition (IHI) from the contralateral M1 to the ipsilateral M1 was assessed.
- The influence of IHI on SICI was evaluated at rest and during 30% and 70% of maximal voluntary wrist flexion force.
Main Results:
- MEP RCs in the resting hand increased, and SICI decreased with increasing force output.
- IHI decreased with increasing force, and was inversely correlated with SICI.
- IHI modulated SICI, decreasing it at rest and at maximal force, suggesting interaction between inhibitory and facilitatory pathways.
Conclusions:
- Activity-dependent changes in SICI within the ipsilateral M1 and IHI between M1s occur during unimanual force generation.
- Interactions between GABAergic intracortical circuits (SICI) and interhemispheric glutamatergic projections (IHI) contribute to regulating corticospinal output to a resting hand during contralateral force production.
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